A Statistical Examination of Severe Tornadic and Nontornadic Quasi-Linear Convective Systems

QLCSs (Quasi linear convective systems) are most well known for producing straight-line winds, but they can also produce tornadoes, and sometimes even tornado outbreaks. Forecasting whether or not a QLCS will be a prolific tornado producer remains a challenge, however. To hopefully improve these forecasts, 139 instances of QLCSs that produced over 100 reports of wind damage were examined during the period 2006-2016. These QLCSs were then grouped by the number of tornadoes that occurred with them, based on a subjective radar analysis. Care was taken to ensure that any tornadoes attributed to the QLCS were not the result of unrelated convection (e.g., discrete supercells ahead of the primary convective line). Statistics were collected on the annual frequency and seasonality of such systems, as well as on system characteristics, including the frontal nature of the QLCS, the temperature gradient across the gust front, and the system speed. It is expected that QLCSs that formed along strong, fast-moving cold fronts are less likely to produce significant numbers of tornadoes than systems that did not form along such boundaries; it is also expected that majority of significantly-tornadic QLCSs occurred during the cold-season months, when the 0-1 km bulk wind shear is stronger.